4.1.6. Adjusting Parallel Replication After Installation

4.1.6.1. How to Change Channels Safely

To change the number of channels you must take the replicator offline
cleanly using the following command:

shell> trepctl offline

This command brings all channels up the same transaction in the log,
then goes offline. If you look in the
trep_commit_seqno table, you will
notice only a single row, which shows that updates to the slave have
been completely serialized to a single point. At this point you may
safely reconfigure the number of channels on the replicator, for example
using the following command:

shell> tpm update alpha --channels=5
shell> replicator restart

You can check the number of active channels on a slave by looking at the
"channels" property once the replicator restarts.

If you attempt to reconfigure channels without going offline cleanly,
Tungsten Replicator will signal an error when you attempt to go online
with the new channel configuration. The cure is to revert to the
previous number of channels, go online, and then go offline cleanly.
Note that attempting to clean up the
trep_commit_seqno and
trep_shard_channel tables manually
can result in your slaves becoming inconsistent and requiring full
resynchronization. You should only do such cleanup under direction from
Continuent support.

Warning

Failing to follow the channel reconfiguration procedure carefully may
result in your slaves becoming inconsistent or failing. The cure is
usually full resynchronization, so it is best to avoid this if
possible.

4.1.6.2. How to Switch Parallel Queue Types Safely

As with channels you should only change the parallel queue type after
the replicator has gone offline cleanly. The following example shows how
to update the parallel queue type after installation: